1. Field of the Invention
The present invention relates to a magnetic storage medium suitable for a magnetic disk unit for performing recording and regeneration of information.
2. Description of the Prior Art
As recording information, which is dealt with in an information processing apparatus, is increased, it is needed to provide a magnetic storage, which is used as an external storage unit of the information processing apparatus, with a compactness and the more large capacity. For this reason, the magnetic storage needs a magnetic storage medium capable of recording at high recording density.
Generally, a magnetic storage medium has a magnetic recording layer on which magnetic information is recorded. A one bit of magnetic information is represented by a direction of a total magnetization consisting of an assembly of the respective magnetizations of a plurality of ferromagnetic crystal particles existing in a one bit cell of the magnetic recording layer. The respective magnetizations of the plurality of ferromagnetic crystal particles are substantially unified in direction in the state that magnetic information is recorded. However, in the event that the magnetization of the adjacent one bit cell is unified in direction opposite to that of the noticed one bit cell, the direction of the magnetization is reversed through a certain width near a boundary between the adjacent one bit cell-to-one bit cell, but not rapidly changed on the boundary. In an area having such a width, magnetizations oriented in mutually different direction are mixed on a zigzag basis. This area is referred to as a magnetization transitional region. In order to satisfactorily reproduce magnetic information which is recorded on a magnetic recording layer of a magnetic storage medium at high recording density, there is a need to prepare a small width of the magnetization transitional region.
It is known that the width of the magnetization transitional region is narrower as the thickness of the magnetic recording layer of the magnetic storage medium is decreased. Hence, hitherto, there is made an attempt that the thickness of the magnetic recording layer is decreased, and there is proposed a magnetic storage medium having a multiple zone of magnetic recording layer in which the above-mentioned magnetic recording layer is divided with a non-magnetic layer.
However, according to the conventional magnetic storage medium, it is known that as magnetic information is recorded at higher recording density, S/Nm of the recorded magnetic information to the regenerative signal is lowered (the medium noise Nm is increased with respect to the output S of the regenerative signal).
One of the causes of occurrence of the medium noise resides in unevenness of a particle size of the ferromagnetic crystal particles. It is considered that the regenerative output is in proportion to the sum total of the volume of ferromagnetic crystal particles. Hence, as the average particle size of one bit cell becomes large, unevenness of a particle size becomes also large. As a result, unevenness of the regenerative output becomes large and thus the medium noise is increased. Therefore, it is considered that the medium noise Nm of the magnetic storage medium is decreased in such a manner that the particle size of the ferromagnetic crystal particles is controlled in the magnetic recording layer of the magnetic storage medium, so that S/Nm is improved.
In this manner, with the thinner magnetic recording layer and the smaller particle size of the ferromagnetic crystal particles in the magnetic recording layer, a signal representative of magnetic information may be regenerated with higher S/Nm. For example, when the magnetic recording layer is given 10 nm or so in thickness and the particle size is given 8 nm to 10 nm or so in an in-plane direction of the magnetic recording layer, it is considered that even a signal representative of magnetic information recorded in high recording density on the order of 10 G bit/inch2 may be regenerated with high S/Nm.
However, As the thickness of the magnetic recording layer as well as the particle size of the ferromagnetic crystal particles are decreased, energy Kuxc2x7V (anisotropy energyxc3x97volume of particle) representative of a degree of easy orientation of magnetization of the particle into a predetermined direction is reduced. When the energy Kuxc2x7V is reduced, a thermal fluctuation phenomenon wherein a direction of magnetization fluctuates owing to the heat will occur. The behavior of the thermal fluctuation phenomenon is determined by ratio of the energy Kuxc2x7V to thermal energy KBxc2x7T (Boltzmann constantxc3x97absolute temperature). Assuming that the thickness of the magnetic recording layer of the conventional magnetic storage medium and the particle size are given by the above-mentioned values, the ratio becomes a small value of the order of 40 to 100 or so at the room temperature (T=300 K). In a case where the ratio is a small value, there occurs the thermal fluctuation phenomenon in magnetization of each of the ferromagnetic crystal particles. Thus, a magnitude of the recording magnetization on one bit cell consisting of the total sum of pieces of magnetization is attenuated. This is associated with a problem that it is difficult to stably maintain for long time magnetic information represented by the recording magnetization.
In view of the foregoing, it is an object of the present invention to provide a magnetic storage medium capable of recording information at high recording density and also to regenerating the information with a high quality of signal (high S/Nm), and in addition contributing to the elongation of a life span of the recorded information.
To achieve the above-mentioned objects, the present invention provides a magnetic storage medium comprising:
(1) a non-magnetic substrate;
(2) a plurality of magnetic recording layers of ferromagnetism; and
(3) a dividing layer of antiferromagnetism for dividing said plurality of magnetic recording layers from one another through intervening between the magnetic recording layer-to-layer.
According to the magnetic storage medium of the present invention as mentioned above, the plurality of magnetic recording layers of ferromagnetism of the item (2) are divided by the dividing layer of the item (3). Thus, each of the divided individual layers of the magnetic recording layers is thinner as compared with a non-divided magnetic recording layer. Generally, in a magnetic storage medium, a width of a magnetization transitional region of a magnetic recording layer is narrowed with thinner magnetic recording layer. This enhances the resolution which is an index indicative of the limit of the recording density of magnetic information recorded on the magnetic recording layer with respect to a fine regeneration. Consequently, the magnetic storage medium of the present invention as mentioned above is suitable for a medium for recording information at high recording density.
According to the magnetic storage medium of the present invention as mentioned above, the plurality of magnetic recording layers of ferromagnetism of the item (2) are in contact with the dividing layer of antiferromagnetism of the item (3). On the interface of the contact, the exchange interaction acts on between magnetization of the respective magnetic recording layers and magnetization of the dividing layer. The existence of the exchange interaction serves to apparently increase magnetic anisotropy energy Ku of ferromagnetic crystal particles constituting the magnetic recording layer. Thus, the ferromagnetic crystal particles is stabilized in magnetization with respect to thermal fluctuation. Accordingly, magnetic information stored in the magnetic storage medium of the present invention may be stored therein stably for a long time.
In the magnetic storage medium of the present invention as mentioned above, it is preferable that said dividing layer consists of a material having a body-centered cubic structure, and each of said plurality of magnetic recording layers consists of a material having a hexagonal crystal structure and a uniaxial crystal magnetic anisotropy.
Generally, in many cases, the material having a hexagonal crystal structure has a uniaxial crystal magnetic anisotropy due to the symmetry of the crystal, and the material having the uniaxial crystal magnetic anisotropy offers a high orientation of magnetization. Further, generally, the material having a hexagonal crystal structure is easy to be subjected to a hetero-epitaxial growth on the material of the body-centered cubic structure rather than the material of the face-centered cubic structure. The hetero-epitaxial growth causes a high orientation of magnetization to be offered. Hence, the magnetic storage medium according to the above-mentioned preferable structure is excellent in orientation of magnetization. Further, an improvement of orientation of magnetization contributes to an increment of a coercive force Hc and an improvement of the resolution. Thus, it is possible to obtain a magnetic storage medium which is large in coercive force Hc and is high in resolution.
Further, in the magnetic storage medium of the present invention as mentioned above, it is preferable that said magnetic recording layer consists of a ferromagnetic alloy in which at least one element of Cr, Pt and Ta is added to Co.
Co is a ferromagnetic material having a hexagonal crystal structure and also having a uniaxial crystal magnetic anisotropy, and is suitable for a material of a magnetic storage medium. Adding Pt to Co enhances a coercive force Hc, and adding Cr or Ta to Co reduces a medium noise of the magnetic storage medium.
Furthermore, in the magnetic storage medium of the present invention as mentioned above, it is preferable that said dividing layer consists of an alloy in which at least one element of Mn, Ru and Re is added to Cr.
It is assumed that the magnetic storage medium, which is usually used, is used at temperature up to 60xc2x0 C. or so. Also in the magnetic storage medium of the present invention, the dividing layer of the item (3) referenced above maintains the antiferromagnetism until at least the same temperature, and thus, as Nxc3xa9el temperature of the material constituting the dividing layer, 400 K is a standard.
As mentioned above, the feature that the dividing layer consists of an alloy in which at least one element of Mn, Ru and Re is added to Cr makes it possible, as will be described in the preferred embodiment of the present invention, to control Nxc3xa9el temperature of the material to be 400 K or more. Further, it is considered that a magnitude of the above-mentioned exchange interaction is varied in accordance with the control of Nxc3xa9el temperature, so that a stability of the magnetic storage medium of the present invention for the thermal fluctuation is increased.
Hereinafter, there will be explained a magnetic storage medium having a Cr system of dividing layer consisting of an alloy in which at least one element of Mn, Ru and Re is added to Cr.
In the magnetic storage medium having the above-mentioned Cr system of dividing layer, it is preferable that said dividing layer consists of an alloy in which Mn of concentration between 5 at % and 80 at % is added to Cr.
The alloy, in which Mn of concentration between 5 at % and 80 at % is added to Cr, is associated with Nxc3xa9el temperature 400 K or more, as will be described in the embodiment of the present invention, and is a material which chemically stably exists. Thus, such an alloy is suitable for the dividing layer.
In the magnetic storage medium having the above-mentioned Cr system of dividing layer, it is preferable that said dividing layer consists of an alloy in which Ru of concentration between 2 at % and 18 at % is added to Cr.
The alloy, in which Ru of concentration between 2 at % and 18 at % is added to Cr, is associated with Nxc3xa9el temperature 400 K or more, as will be described in the embodiment of the present invention. Thus, such an alloy is suitable for the dividing layer.
In the magnetic storage medium having the above-mentioned Cr system of dividing layer, it is preferable that said dividing layer consists of an alloy in which Re of concentration between 2 at % and 14 at % is added to Cr.
The alloy, in which Re of concentration between 2 at % and 14 at % is added to Cr, is associated with Nxc3xa9el temperature 400 K or more, as will be described in the embodiment of the present invention. Thus, such an alloy is suitable for the dividing layer.
In the magnetic storage medium having the above-mentioned Cr system of dividing layer, it is preferable that said dividing layer consists of an alloy in which at least one element of Mo and W is added to Cr.
In the magnetic storage medium having such preferred structures as mentioned above, an interval between (110) face and (110) face of the alloy in which at least one element of Mo and W is further added to Cr, which alloy constitutes the dividing layer, is controlled by an amount of added Mo and W. In the event that the plurality of magnetic recording layers of the item (2) consist of an alloy of which a main component is Co excellent as a ferromagnetic material, an interval between the above-mentioned face-to-face is controlled so as to substantially coincide with an interval between (002) face and (002) face of the alloy in which Co is a main component. This control contribute to acceleration of a hetero-epitaxial growth between the recording layers and the dividing layer. Consequently, the magnetic storage medium is favorable in orientation, large in coercive force Hc and high in resolution.
In the magnetic storage medium having the above-mentioned Cr system of dividing layer, it is preferable that said dividing layer consists of an alloy in which at least one element of Pt and Rh is added.
Adding those elements to Cr makes it possible to increase a thermal stability of the magnetic storage medium as will be described in the embodiment of the present invention.
In the magnetic storage medium having the above-mentioned Cr system of dividing layer, it is preferable that said alloy has Nxc3xa9el temperature 400 K or more.
In an alloy constituting a dividing layer, also in the event that a plurality of elements are added to Cr, if an amount of addition of elements is controlled in such a manner that the alloy has Nxc3xa9el temperature 400 K or more, it is possible to provide a magnetic storage medium suitable for practice use.
Next, there will be explained a magnetic storage medium having a primary layer.
In the magnetic storage medium of the present invention as mentioned above, (4) it is preferable that the magnetic storage medium further comprises a primary layer composed of at least one of a non-magnetic layer consisting of a material having a body-centered cubic structure and an antiferromagnetic layer consisting of a material having a body-centered cubic structure, said primary layer being adjacent to said substrate, wherein a lowest stage of magnetic recording layer of said plurality of magnetic recording layers is formed adjacent to said primary layer.
The magnetic storage medium having a primary layer is excellent in orientation of magnetization since the magnetic recording layers of the item (2) are favorably subjected to the hetero-epitaxial growth on the primary layer. Further, in a case where the primary layer includes an antiferromagnetic layer, the antiferromagnetic layer is in contact with the lowest stage of magnetic recording layer of the plurality of magnetic recording layers. This feature makes it possible to hold magnetic information recorded on the magnetic storage medium of the present invention stably for a long time.
In the magnetic storage medium having the primary layer, it is preferable that said primary layer has said non-magnetic layer, and said non-magnetic layer includes Cr and consists of a material in which Mo or W is added to Cr.
The magnetic storage medium having the above-mentioned structure is favorable in orientation, large in coercive force Hc and high in resolution by the same reason as a case where said dividing layer consists of an alloy in which at least one element of Mo and W is added to Cr.
In the magnetic storage medium having the primary layer, it is preferable that said primary layer has said antiferromagnetic layer, and said antiferromagnetic layer includes Cr and consists of an alloy in which at least one element of Mn, Ru and Re is added to Cr.
The magnetic storage medium having the above-mentioned structure is capable of controlling Nxc3xa9el temperature to be 400 K or more by the same reason as a case where said dividing layer consists of an alloy in which at least one element of Mn, Ru and Re is added to Cr. Further, it is possible to increase a stability as to a thermal fluctuation of the magnetic storage medium of the present invention.
Hereinafter, there will be described the primary layer having the antiferromagnetic layer which includes Cr and consists of an alloy in which at least one element of Mn, Ru and Re is added to Cr. The antiferromagnetic layer of the primary layer of the respective magnetic storage medium having the preferable structure, which will be described hereinafter, has the similar aspect to the above-mentioned dividing layer having the same structure as the antiferromagnetic layer.
In the magnetic storage medium as mentioned above, wherein said primary layer has said antiferromagnetic layer consisting of said alloy, it is preferable that said antiferromagnetic layer includes Cr and consists of an alloy in which Mn of concentration between 5 at % and 80 at % is added to Cr.
In the magnetic storage medium as mentioned above, wherein said primary layer has said antiferromagnetic layer consisting of said alloy, it is preferable that said antiferromagnetic layer includes Cr and consists of an alloy in which Ru of concentration between 2 at % and 18 at % is added to Cr.
In the magnetic storage medium as mentioned above, wherein said primary layer has said antiferromagnetic layer consisting of said alloy, it is preferable that said antiferromagnetic layer includes Cr and consists of an alloy in which Re of concentration between 2 at % and 14 at % is added to Cr.
In the magnetic storage medium as mentioned above, wherein said primary layer has said antiferromagnetic layer consisting of said alloy, it is preferable that said antiferromagnetic layer includes Cr and consists of an alloy in which at least one element of Mn, Ru and Re is added to Cr, and in addition at least one element of Mo and W is added.
In the magnetic storage medium as mentioned above, wherein said primary layer has said antiferromagnetic layer consisting of said alloy, it is preferable that said antiferromagnetic layer includes Cr and consists of an alloy in which at least one element of Mn, Ru and Re is added to Cr, and in addition at least one element of Pt and Rh is added.
In the magnetic storage medium as mentioned above, wherein said primary layer has said antiferromagnetic layer consisting of said alloy, it is preferable that said antiferromagnetic layer includes Cr and consists of an alloy in which at least one element of Mn, Ru and Re is added to Cr, said alloy having Nxc3xa9el temperature 400 K or more.
In the magnetic storage medium of the present invention as mentioned above, (5) it is preferable that the magnetic storage medium further comprises a protective layer including a carbon, said protective layer being formed adjacent to a top layer of said magnetic recording layers.
In the case of this magnetic storage medium, since the protective layer of the item (5) consists of hard particles, the magnetic recording layers of the item (2) are protected by the protective layer.
In the magnetic storage medium of the present invention as mentioned above, it is preferable that said magnetic recording layers are associated with a product Brxc2x7t between 20 Gaussxc2x7xcexcm and 100 Gaussxc2x7xcexcm where Br denotes a residual flux density of the magnetic recording layers and t denotes a sum total of thickness of the magnetic recording layers.
In the magnetic storage medium which is usually used, the value of Brxc2x7t is 100 Gaussxc2x7xcexcm or so. Thus, in order to improve a resolution of the magnetic storage medium, it is preferable that a sum total of thickness of the magnetic recording layers is reduced so that the value of Brxc2x7t is not more than 100 Gaussxc2x7xcexcm. On the other hand, in the magnetic storage medium wherein the value of Brxc2x7t is not more than 20 Gaussxc2x7xcexcm, it is difficult to obtain a sufficient regeneration output with the use of a head which is usually used. For this reason, it is preferable that the value of Brxc2x7t is not less than 20 Gaussxc2x7xcexcm.
In the magnetic storage medium of the present invention as mentioned above wherein each of the plurality of magnetic recording layers consists of a material having a uniaxial crystal magnetic anisotropy, it is preferable that said substrate is a disk-like shaped substrate, and said magnetic recording layers are associated with one in which a direction of a uniaxial crystal magnetic anisotropy of a material constituting each of said magnetic recording layers is substantially coincident with a circumferential direction of the disk-like shaped substrate.
Generally, a magnetic storage medium is of a disk type, and a direction of a magnetic field of a head for recording magnetic information on the magnetic storage medium or regeneration of the magnetic information is substantially coincident with a circumferential direction of the disk-like shaped magnetic storage medium. As will be described in the preferred embodiment of the present invention, magnetic information of the magnetic storage medium is held more stably on a thermal basis with greater magnetic anisotropy in a circumferential direction of the disk-like shaped magnetic storage medium.